I've always felt strong and fit in my body. For workouts, I ride 30-plus miles on my bike, swim half a mile, and regularly rotate between barre, yoga and Spin classes. I've never paid much attention to the scale. I believed that since I was exercising and making (mostly) healthy food choices, I didn't need to focus on weight. Right?

Then a dress felt snug before a friend's wedding last spring. I blamed it on hormones, too much salt, even the innocent dry cleaner. I had become blind to the fact that I'd been relying on Spanx and flowy dresses rather than realize my clothing wasn't fitting right. So I stepped up my workouts and eliminated processed carbs. I skipped dessert and avoided alcohol. But six weeks later I still had a pouch.

That's how I ended up in the Manhattan office of dermatologist Dr. Dennis Gross, M.D. with a device the size of an ostrich egg sitting on my stomach. I was there to test out UltraShape, a recently FDA-cleared machine that promises to blast away stubborn fat—the subcutaneous type that exercise and diet alone can't tackle.

Unlike other popular body contouring procedures, UltraShape doesn't require extreme heat or cold to destroy fat: instead, it harnesses ultrasound waves, which "shake the fat cells until the membranes collapse," explains Dr. Gross. Then the destroyed fat cell particles are filtered through the liver and digested through the body—just like fat from a meal. Interestingly, this process doesn't harm any of your tissues, blood vessels or nerves, so there's no recovery time. For that reason, Dr. Gross considers UltraShape a "game-changer" in nonsurgical treatments.

"When you look at before-and-after images of patients, the results from UltraShape are visually impressive," he tells me before we get started. In several small studies, subjects who did three treatments typically lost between one and two inches from their stomachs after six weeks. That beats the 8 to 12 weeks associated with other popular sculpting treatments, like Liposonix or CoolSculpting.

Still, UltraShape is not a magic bullet, or substitute for balanced eating and fitness habits. "This is not a treatment for obesity," points out New York City dermatologist Bruce Katz, M.D., who has been using the device in his office for a year. "But it can create contours and reach fat that is challenging to reduce with exercise," he says. While it's FDA-approved for use on the stomach and love handles, Dr. Gross warns that UltraShape can't fix all problem spots. "If you have separated muscles or loose skin from pregnancy, UltraShape won't work as effectively on those areas," he says.

My main concern: Would it hurt? Dr. Gross assured me it would not. (I didn't even need to apply a numbing cream beforehand.) He started the process by creating a 3-D map of my stomach with a high-tech camera and computer. Then I lay back—and prepared for shocks, tugs, burns or some sort of discomfort—but I didn't feel anything other than the weight of the transducer gliding over my torso. Each time the device buzzed, I imagined hundreds of fat cells being pulverized. As the device targeted the layer of stubborn fat, I was so calm I could have meditated.

An hour later I was done. There was no pain, soreness, redness or signs of bruising. Dr. Gross told me to drink lots of water and eat as clean as possible for the next 36 hours to help my body process the destroyed fat cells. "You have to do your homework—exercise and eat healthy—or you won't see a big change," he told me.

Even without his instructions, I would have been motivated to treat my body well: I attacked my daily workouts with even more enthusiasm as I started to visualize fat dissolving. I became vigilant about what fuel I needed and how anything junk-y would negate the effects of UltraShape. I bought kale in bulk.

Two weeks later I went back for my second treatment. My measurements revealed I'd only lost a couple millimeters (!). So far, the only thing deflated was my pride. Dr. Gross had warned me that the biggest results would kick in four to six weeks after the initial treatment. I reminded myself to be patient. In the meantime, I stuck with my workouts and cooked like Gwyneth.

A week later—and three weeks after my first session—I noticed something new: During a swim workout, my suit felt lose, which seemed odd because it was too new to have lost stretch.

My suspicions were confirmed when I arrived for my third appointment with Dr. Gross: I'd lost nearly two inches on my upper abdomen and just over two on my lower stomach. And I gained a completely new perspective on my closet. I held my breath as I effortlessly pulled on a pencil skirt I hadn't worn in at least six months. I now saw possibilities, not excuses, in my closet.

Three UltraShape sessions and six weeks later, I've lost about eight pounds and just over two inches around my lower stomach. No doubt, diet and rigorous exercise played a part—but UltraShape just helped slightly contour me in a way that I hadn't been able to do with planks or swimming drills. And now it's up to me to maintain the results. Bring on the kale smoothies!